In recent years, in fields of servers, high performance computers (HPC), and the like, an improvement in performance due to the multi-CPU compatibility dramatically increases the transmission capacity of I/O functions communicating between a CPU and an external interface. Meanwhile, as a related technique, there is a limitation in high speed transmission by an electrical signal from the perspective of occurrence of crosstalk and wiring density. With that, a technique (optical interconnection technology) that achieves high speed I/O with a signal light by disposing a photoelectric transducer is under study.
The number of optical transmission paths used for servers and high end computers is enormous, and the number of optical modules thus used also becomes large. Therefore, modules for optical interconnection are desired to be low in costs in comparison with modules for long distance optical communication.
In an optical interconnector, while the multi-channel parallel optical connection technique is employed for using a VCSEL (vertical cavity semiconductor emission laser) array as a light emitting element and a PD (photo diode) array as a light receiving element in general, there is also an increasing demand for cost reduction to multi-channel optical connectors. In the multi-channel optical connectors, with an increase in the transmission capacity, it is desired to increase the number of channels from the current mainstream 12 channels to 24 channels and further to 48 channels.
As a connector for optical fibers in a related technique, an MT (mechanical transferable) connector is known. An MT connector is achieved by inserting optical fibers into an MT ferrule and aligning the axes to maintain the optical path in a straight line and by polishing end faces of the optical fibers. However, in the step of polishing, a polisher is used and a plurality of polishing sheets is replaced, so that the time and the costs increase. Therefore, it is strongly desired to develop multi-channel optical connectors without polishing.
As a technique to implement optical fibers without polishing, there is a known technique that configures optical connectors with ferrules of a transparent material and presses cut end faces of the optical fibers against a vertical wall formed in the ferrule for implementation (for example, Japanese Laid-open Patent Publication No. 2009-258510). The optical fibers are cut using a fiber cutter. A beam emitted from the optical fibers pressed against the transparent wall has the optical path bent 90 degrees with a concave mirror.
As another example of the no polish implementation technique, there is a known technique that adheres and fixes a fiber optical plate (FOP) to a front face of the ferrule, and then inserts connecting ends of the optical fibers into the ferrule while the end faces are still unpolished and presses the unpolished end faces of the optical fibers against the FOP for connection (for example, Japanese Patent No. 3364638). The FOP used for this method is an optical component made by bundling a large number of optical fibers and stretching them to be sliced thinly.
All of the optical connectors using no polish optical fibers in the related techniques have a configuration of pressing cut end faces of fibers against a wall. When actually manufacturing no polish optical connectors on mass production lines using a related technique, the following problems arise.
Firstly, there is influence of dust collection mixed during ferrule manufacture and assembly. As illustrated in FIG. 1A, when inserting cut no polish optical fibers 113 into a ferrule 121, there is a possibility of mixing dust collection (dust) 105 in the 100 μm order into an insertion hole 122. As illustrated in FIG. 1B, in a case that the optical fibers 113 are pressed against an FOP 130 and the dust 105 is attached on an end face of a core 111, a light passing through the core 111 is scattered at the dust 105 to be a factor of a loss. Although the dust 105 does not mix into in all cases, it is difficult to be thoroughly removed, and in a case that the dust 105 attaches to the core 111 in even one of the plurality of channels, an optical loss occurs in that channel, which makes the entire optical connector defective. As a result, the manufacturing yield decreases. This problem becomes more apparent as the number of channels in an optical connector increases.
Next, when reducing the influence of dust in a no polish connector, it is desired to take measures, such as to carry out the assembly step in a clean room environment. In contrast, in the current mainstream MT connector, the tip ends of the optical fibers are polished after inserting the ferrule, so that the influence of dust does not become a problem and a clean room is not used. Accordingly, a no polish connector takes a lot of equipment investment and becomes disadvantageous in costs compared with the polished MT connector and the like. In a case of a no polish connector, it is difficult to achieve cost reduction if not enabling manufacture in an environment same as the polished connector.